Associate Editor, Marc-André Villard discusses the tricky business of managing nest predation and the recent article by Chiavacci et al. Linking landscape composition to predator-specific nest predation requires examining multiple landscape scales.

Predation is, by far, the main cause of nest failure in songbirds.  Therefore, it is important to understand the factors putting certain species (or their nests) at risk.  For decades, researchers have tried to identify the factors determining nest predation risk, mainly focusing on the victims and examining the influence of nest height, concealment by vegetation, or nest type.  In this article, Chiavacci et al. turned the cameras on the culprits.  They monitored 468 nests of shrubland birds using video-cameras and caught 212 predators in the act, including 26 species of birds, mammals, or snakes.  Of these, seven species of predators were frequent enough to offer a more detailed glimpse into their own world.

The diversity of species responsible for nest predation events implies that no single management action will ever protect all nests of a focal species.  For example, in the U.S. Midwest, managers have to consider nest predators as distinct as Cooper’s Hawk and Fox Snake.  However, pairs of predator species that might be expected to have a similar influence on nest predation risk, such as Fox and Black rat Snake, actually responded very differently to landscape structure.

Nest Robbers Spring Squirrel Verifiable Kitten
‘In the shrub-nesting birds under study, risk decreased with nest height for several important predators, but it increased for squirrels’.

Anthropogenic activity, quantified through the proportion of agricultural or urbanized land, has often been linked to nest predation risk.  Early studies suggested a strong increase with proximity to developed land, because human activities provide extra food to opportunistic, omnivorous nest predators.  Here again, the authors report that reality is not that simple.  The Raccoon, a well-known suburban opportunist, actually responded positively or negatively to developed cover, depending on the spatial scale considered.

This study does not simply illustrate the complexity of the cat-and-mouse game played by songbirds and their nest predators.  Some parameters provided reliable information on nest predation risk.  In the shrub-nesting birds under study, risk decreased with nest height for several important predators, but it increased for squirrels.  Interestingly, parameters such as nest concealment by vegetation or nest stage had little influence on nest predation risk.

In a nutshell, Chiavacci et al.’s findings stress the fact that effective management of nest predation on focal bird species starts with identifying the main predator species involved.  However, removing a nest predator from the equation may simply open the door to others and, therefore, continuous monitoring is required to find out whether the nest predation rate actually decreases.  If not, managers must determine what predator species are involved.  Removing a nest predator that controls populations of other nest predators may also be counterproductive.  Hence, managing nest predation is no simple matter, but at least the authors give us a clear roadmap on the critical steps to be taken to tackle this complexity.

Read the full article, Linking landscape composition to predator-specific nest predation requires examining multiple landscape scales in Journal of Applied Ecology.

 

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